Manufacture of grease-resistant paper



- Patented Dec. 8, 1942 UNITED STATES- PATENT OFFICE Milton 0. Schur,Berlin, N. 11., assignor, by mesne assignments, to ReconstructionFinance Corporation, Washington, D. 0., a corporation oi." the UnitedStates of America Application March 23, 1939, Serial No. 263,664

13 Claims.

This invention relates to the manufacture of grease-resistant paper andmore especially of paper such as is to serve in the food-wrapping andfood-packaging art for such purposes as lining bags, boxes, or othercontainers for greasy or oily comestibles of the nature of coffee,cocoa, peanuts, potato chips, cookies, crackers, etc. Thegrease-resistant or greaseproof paper product hereof may be used toadvantage as a liner in an ordinary paper bag or in a box or containerof the usual paperboard variety. It may also be used by itself, that is,without an external wrapping, bag, or container, as a food-wrapping orfood-packaging medium.

Such grease-resistant papers as have heretofore been available forfood-wrapping or foodpackaging purposes are quite expensive. This isespecially true of parchment paper and is also true of glassine paper,which latter paper is so brittle and deficient in flex-endurance andtearduring machine-fabrication or filling of the package or once thepackage in which it serves as a liner has been opened. and the liner isexposed to handling,

The present invention provides at comparatively low cost a greaseproofpaper product that is not only serviceable in lieu of glassine andparchment papers in the food-wrapping and food-packagin art but that isalso characterf ized by much higher flex-endurance and tearresistancethan glassine paper. As an illustration, the greaseproof paper producthereof may be supplied to bakeries, wherein it may advantageouslyreplace the more expensive glassine paper for lining the paperboardboxes in which shortened crackers, cookies, and other bakery productsare packed and sold, As another illustration, the greaseproof paperproduct hereof may be sold to cofiee-packing establishments, wherein itmay be used instead of the more expensive greaseproof' papers heretoforeused in making the liner bag of a two-ply paper bag for holding andvending coffee. Indeed, if the outer coffee bag is prepared from paperaccording to the present invention, the inner bag may be dispensed with,thereby lending a substantial saving in the cost of the package.

In producing. the greaseproof paper product hereof, an ordinarynon-grease-resistant paper base, such as bleached or unbleached kraftpaper, may serve as the starting material. The paper base, which maycontain, if desired, a small amount of such usual sizing material asrosin, starch, or the like, is preferably primed on at least one surfacewith a composition containing bentonite and preferably also a suitablebinder, such as cooked starch, casein, glue, etc. After the papersurface has been primed with an aqueous priming composition containingbentonite and water-soluble binder and the primed surface has beendried, the resulting primed surface is resistance as to be apt to befractured or torn talc, calcium carbonate, or the like, it is muchcoated with rain or equivalent grease-resistant I prolamine in the formof a solution in a suitable volatile organic solvent, such as ethylalcohol, and the coated surface dried. Only an extremely thin coating ofthe zein on the preferably bentonite-primed paper surface is necessaryfor developing a finished paper product of remarkably highgrease-resistance.

The priming of the paper surface with bentonite composition is preferredin that it facilitates the realization of the desired grease-resistantor grease-proof paper product hereof.-

Thus, when priming of the paper surface is effected with other fillingor priming compositions, such as compositions containing ordinary clay,

more difficult to produce a paper product of unimuch zein issubsequently applied as a coating to the primed surface as to renderless feasible economically the manufacture of a paper productcompetitive with glassine paper. .It is evidently the case that thecolloidal clay known as bentonite is outstanding in its ability todeposit within the pores on a normal paper surface a priming film ofsuch tightness, continuity, or fine texture that it can take on a verythin zein coating practically free from such gaps, disruptions,orpinholes as would detract seriously from or vitiate the greaseproofquality desired in the finished paper product. Again, the desiredgreaseproof quality is attained in the finished paper product hereofwhile using only such small paper. Along with the bentonite as thepriming substance, it is preferred to use cooked starch as the binder,for the combination of bentonite and cooked starch in the primingcomposition has been found to give excellent results. Thus,

' a priming composition containing bentonite and cooked potato starchhas been found to be much better for the purposes hereof than a primingcomposition containing bentonite and such other binders as casein, glue,etc.

' While not limited thereto, I shall now give a typical example ofprocedure leading to a greaseproof paper product which resists for verylong periods of time penetration by grease, for instance, when put tosuch exacting service as the liner bag of a two-ply paper bag forholding and vending ground coffee. Such procedure will be described withreference at the appropriate time to the accompanying drawing, whereofFigure 1 illustrates diagrammatically and conventionally preferredinstrumentalities, including a pair of rolls, for applying the zeinsolution to the primed paper sheet and Figure 2 represents a fragmentarysection through the rolls as the paper sheetis passing therebetween andis receiving a coating of the zein solution.

The paper base used as the starting material may be a rosin-sized kraftpaper sheet of the ordinary wrapping paper type composed of wellbeatenpulp and having a basis weight of, say, about to pounds (i. e., theweight in pounds of a ream of 480 sheets, 24:" x 36"). The expressionwell-beaten pulp as used herein means that, although the pulp has beenbeaten to a stage well beyond that customary in the manufacture of, say,ordinary wrapping paper, it is none the less at a stage of hydration orgelatinization far short of that developed in glassine papermanufacture. The sheet may be run continuously either from a'rollaccumulation or from the dry end, of a papermaking machine through anordinary size-press or tub containing the priming composition hereof. Asatisfactory priming composition for the purposes hereof may consist ofan aqueous suspension of about 3% bentonite and about 3% cooked potatostarch. The size-press may be operated to apply the priming compositionto either or both faces of the sheet. Ordinarily, however, it isdesirable to apply the priming composition to both faces of the sheet,since the composition is comparatively inexpensive and only a very smallamount need be deposited on the sheet and infused into its surfacepores. In such latter case, the sheet may be progressively led throughthe bath of priming composition and thence into the nip of the pressrolls forming part of the size-press. Pursuant to such operation, sheetas it issues primed on both its faces from the size-press may have takenup about 0.5% to 2% bentonite and about 0.5% to 2% starch, based on thedry weight of the starting sheet.

The primed sheet issuing from the size-press the sheet at the'nip, asmall bank of solution being constantly maintained at the front oringress of the nip. It is desirable to prevent a coating of dried zeinfrom building up on the upper roll periphery by reason of evaporation ofsolvent from the film of zein solution remaining on such periphery asthe sheet leaves it. While this may be done by housing the upper the vThe dried, primed paper sheet may .paper surface.

roll in a suitable metal enclosure, it is accomplished simply andadvantageously, as illustrated in Figure 1, by causing the paper sheetas it leaves the nip to wrap over the top roll for as much of itsperiphery as possible, preferably a peripheral surface of about ormore.

It will be observed from Figure 1 that the primed paper sheet S isprogressively passed at an angle upwardly into the nip of the pressrolls III in front of which is maintained a small bank B of the zeinsolution. The zein solution may be continuously fed onto the upper papersurface from a nozzle ll whose discharge end I! is disposedsubstantiallycentrally and immediately in front of the nip and slightly above the Thesolution may be carefully metered or regulated in its flow onto thepaper so as to maintain the bank B of substantially constant sizesufllcient to coat the paper sheet substantially uniformly throughoutits entire width or upper surface and at the same time to avoidappreciable overflow or extrusion of solution beyond the paper edges. Itis preferable that one of the two rolls in be peripherally covered witha yielding or resiliently soft substance, for example, soft rubber, andthat the other roll present a hard peripheral surface, for example, asmoothly polished steel 'surface. As shown, the lower roll has asoft-rubber periphery "a,

whereas the upper roll has a smooth steel perlph cry. The upperroll maybe urged or pressed against the paper by a dead weight or by springs inthe usual manner.

The soft-roll periphery ensures uniform pressure between the paper sheetand the hard rollperiphery and thereby fosters the deposition of asubstantially uniform coating of zein solution on the preferably primedpaper sheet. When it is realized that a paper sheet normally varies inthickness at least a fraction of a thousandth of an inch and that thezein coating is of a thickness amounting to a fraction of a thousandthof an inch, the desirability of providing substantially uniform pressureover the entire upper sheet surface, as it is being coated with zeinsolution, is at once recognized.

It is highly desirable that the sheet entering the nip between rolls in,i0 wrap the lower rollv for a material distance so as to seal the edgesof the paper sheet and thereby prevent the coated solution from runningunder the sheet edges. If such running of coating solution under thesheet edges were permitted, not only would needless waste of relativelyexpensive coating solution be occasioned, but the roll of paper sheetfinally accumulated at the end of the zein-coating machine would lackuniformity in that the edge portions of the sheet would be much harderthan the rest of the sheet; and the edge portions would tend to sticktogether or block" with attendant difliculty in unwinding the sheet fromthe roll.

As illustrated in Figure 1, the sheet S, as it is being coated with thezein solution, wraps thelower roll l0 so that the bank of coatingsolution II cannot creep' under the sheet edges; and such wrap of thelower roll by the sheet is over a substantial arc, say, upwards of about10, the particular arcuate angularity or extent of the wrap dependingupon the size of the roll. In order to realize maximum benefit from thewrap on the lower roll l0, it is desirable to station the two rolls withtheir axes in the same vertical plane or with the axis of the upper rollsomewhat onset in the direction of traveLof the paper sheet through thenip. The long wrap of the paper 2,304,987 'sheet about the upper rollperiphery avoids such long-time exposure of the residual film ofzeinsolution on such periphery as would be attended by drying and setting ofsuch film.

Although zein solution as it is applied to the paper sheet may vary inits concentration and contain various volatile organic-solvents of zein,it preferably consists of a zein solution of about 20% to 25% strengthor concentration in ethyl alcohol. Such a solution has a consistency orviscosity appropriate for coating at about room temperature thepreferably primed paper sheet by the particular and advantageous methodjust described. The conditions of coating are prefer.- ably such as todeposit the zein on one face of the paper sheet in amount of only about1 to 2 pounds per ream (2880 square feet) of paper. Indeed, with anappropriate base paper. sheet and an appropriate priming treatment, itis possible to arrive at the greaseproof quality desired in the finishedpaper product hereof with a zein coating composition applied to only oneface and amounting, on a dry basis, to as low as about 0.4 pound of suchcomposition per ream of paper.

The paper sheet thus thinly coated with zein solution may beprogressively run through an airdrier, for instance, through a warm-airtunnel, to promote complete removal of the ethyl alcohol solvent. Theresulting zein-coated paper sheet may then be wound in rolls and shippedto the consumer. It has been found that when such sheet is used as theliner bag of a two-ply paper bag for holding ground coffee, itsgreaseproofness is such that no stain is visible on the exterior surfaceof the liner even after its interior or zein-coated surfacehas been incontact with its ground coffee contents for many months. It

might be noted that the greaseproof paper product hereof can be handledin the usual bag-feeding,- bag-folding, an pasting equipment without theslightest difficulty; and the finished bag may without danger of tearingor other difilculty be filled with coffee or other comestibles byautomatic bag-filling machinery. It will be appreciated, of course, thatthe paper product herein might be coated with zein on both its faces,but it is usually desirable from the standpoint of economy to coat withzein only the face of the paper product to come into contact with greasyor oily comestibles.

In one example of procedure, kraft. pulp was beaten to a Canadianfreeness of 350 cc. and then was converted into 25'-pound paper (weightper 2880 sq. ft.) in the conventional way on a Four- I drinier machine.The paper showed an oil resistance of only 5 seconds on the wire sideand seconds on the top or so-called web side. The sheet was then passedthrough a size press wherein it was treated with an aqueous mixture ofbentonite and cooked potato starch containing 3% of each. After it hadbeen redried it showed an oil resistance of 35 and 110 seconds on thewire and web" sides, respectively. The oilresistance values weredetermined by noting the time for lubricating oil of S. A. E. viscosity30.

to break through the sheet over about 90% of the surface of 1 inchsquare specimens floated on the oil at .70 F. A zein solution was thenapplied to the web side of the bentonite treated sheet, and, althoughonly 1.7 pounds of dry coating was deposited per ream (2880 sq. ft.),the sheet was substantially oil-and-turpentine-proof.

The web"- side of the sheet was coated, since this side usually givesthe better result with regularity. In a second case, the pulp was beatento being coated with zein.

a freeness of 225, the 28-pound paper made from it had an oil resistanceof 25 seconds on the wire side and 90 seconds on the web side, prior tothe bentonite-starch tubbing, and an oil resistance of 70 and 250seconds on the corresponding sides after the tubblng and redrying. Whenthe web side .was coated with only 1.2 pounds, dry basis, of a mixtureof 3 parts of zein and 1 part of invert sugar deposited from an alcoholsolution containing a small proportion of water, it was substantiallyoil-and-turpentine-proof. When to the bentonite-starch tubbing mixturesa little ammonia water or equivalent defiocculating agent is added, theoil resistance of the tubbed sheet is even higher than above indicated.In any case,it is significant that the ash-content of the paper wasincreased less than about 1%% when the sheet was primed with thebentonitestarch mixture, and thatno coating of bentonite or starch wasvisible on the paper prior to its' In lieu of bentonite, it is possibleto use for the purpose ofpriming the paper surface an appropriatelycolloidal clay, preferably a colloidal clay that has been additionallypeptized in water containing ammonia or equivalent clay defiocculatingagent. The use for the paper-priming purposes hereof of the colloidalfraction of china clay, for instance, such fraction as is separated fromthe whole clay by an electrophoretic fractionating method, together withammoniated water as the suspending medium for such fraction leads toresults somewhat similar to those had from bentonite; and the term"bentonite as used in the appended claims is meant to include suchcolloidal clay fraction. However, bentonite as terized by the firmnessor high tenacity of its I .etc.

such is generally to be preferred because of its lower.cost and theconsistently excellent results realized therefrom. Again, it is possibleto use in lieu of zein on the bentonite-primed paper surface such othergrease-resistant, film-forming,

solid substances as nitrocellulose, acetylcellulose,

bond with the primed paper surface, insomuch thatsuch coating or filmhas practically no tendency to peal or break away from the paper base inth course of handling the greaseproof paper product hereof 'or offabricating it into liner bags,

liners, etc.

Because of the extreme thinness of the zein coating solution on thepreferably primed paper sheet hereof, the tendency for curlingof suchpaper sheet during its drying is min mized. Such minimization of curlingis-especially important in the case of thin or lightwe ght paper bases,

whose res stance to curling is low, especially when the finished paperproduct hereof is intended to be cut into fiat sheets or blanks forlining paperboard boxes. -It is, moreover, possible to incorporate intothe zein solution plasticizing agents, such as invert sugar, glycerine,ethylene glycol,

and other substantially non-volatile alcohols or glycols that serve tooffset curling tendency in the finished paper product hereof.

The zein-coated paper product hereof lends itself particularly well tocoating very thinly with wax, such as paraflln, to yield a paper producthighly resistant to the passage of water vapor therethrough. Thus, thepaper product hereof may be made remarkably moistureproof as well asgreaseproof' by being coated on its zein-coated face with moltenparaflin wax or its equivalent in amount as little as about 2 to 4pounds of paraffin wax per ream. The reason why such small amounts ofwax are effective in contributing high moisture-impermeability to thewaxed paper product hereof is. because .the zein coating on such productkeeps the paraffin wax practically entirely on the paper surface, thatis, prevents the wax from being dissipated into the body of the papersheet. In some instances, it

may be desirable to produce a paper product waxed on both its faces, asby running the zeincoated base' paper sheet through a bath of moltenparaflin wax. In such instances, th preferably primed paper sheet-isadvantageously coated with the zein composition on both its faces, asby" running the preferably primed paper sheet through a bath of the zeincoating composition or by spreading such composition first on one faceand then on the other. The resulting paper product waxed on both itsfaces may carry no more than about -2 to 4 pounds ofpara'flin wax perream of paper in acquiring the desired high moistureproofness. It mightbe noted that the application of the zein composition and wax to bothsurfaces of the paper sheet minimizes tendency for the paper product tocurl, since such shrinking or curling forces as may be incident to theapplication of the zein composition and/or wax to one face of the sheetare substantially neutralized by similar forces incident to theapplication of the zein composition and/or wax to the other face bf'thesheet. v

- The improvement in the oil or grease-resistance of the base papereffected by the bentonitestarch. composition or tubbing is importantbecause it makes possible, by keeping the filmforming medium practicallyentirely on the surface, the attainment of substantially completeimperviousness with an exceedingly small quanprimed with thebentonite-binder composition, a

finished paper sheet of the desired greaseproof quality even when thegreaseproofing zein coating composition is extremely thin or attenuated,for instance, is spread on one face of the paper sheet in amount rangingfrom only about 0.4 to 2 pounds of the dry zein composition per ream(2880 square feet) of paper. Because the dried The valuable factor ofpriming the base sheet need not, however, necessarily be utilized,provided that the factor of beating or hydrating the pulp entering intothe paper sheet or base is ap propriately correlated with the aspect ofthe zein-coating composition to foster the greaseproof quality desiredin the finished paper product along with such other qualities as thedesired high flex-endurance and tear-resistance.

in realizing the highly greaseproof paper products hereof, spread morezein coating composition than that already indicated as yielding a verythin or highly attenuated film on the paper base,

' for instance, zein coating composition amounting on a dry basis to nomore than about 0.4 to about 2 pounds per ream surface (2880 squarefeet). As already indicated, such a very thinly zeincoated paper producthas the desired high flexenduring and tear-resisting qualities coupledwith the desired greaseproofness.

The terms "greaseproof or grease-resistant," as used in the foregoingdescription and in the appended claims in characterizing a paper producthereof, mean that such product shows no sign of oil-staining oroil-leakage when such product is subjected to the so-called turpentinetest. This test is conducted by supporting the paper product specimenwith its zein-coated face up on a sheet of white absorbent paper,placing on such upper face a. small mound of fine sand, and adding tothe sand a slight excess of moisture-free turpentine containing a smallamount of a suitable dye. After about 4 to 6 hours, the specimen islifted from the underlying absorbent paper support. Should the absorbent'paper support display no sign of staining by the dyed turpentine, thespecimen is considered to be greaseproof. It might be noted, however,that the greaseproof or grease-resistant paper products hereof usuallyare vastly more grease-resistant or greaseproof than that necessary tosatisfy such conventional test. Indeed, the products hereof usually showno transmission therethrough of turpentine even after a. test period ofabout 12 to 16 hours.

I claim: I

1. A grease-resistant paper product primed on its surface with bentoniteand cooked starch and filmed on such primed surface withgrease-resistant prolamine.

zein composition exists in such attenuated or thin 2. A grease-resistantpaper product comprising a substantially non-grease-resistant paper baseprimed on its faces with a mixture of bentonite and binder and filmed onat least one primed face with grease-resistant prolamine.

-3. A grease-resistantpaper product primed on its surface with bentoniteand cooked starch and filmed on such primed surface with zein in amountof only about 0.4 to 2 pounds per ream surface (2880 square feet).

4. A grease-resistant paper product comprising a substantiallynon-grease-resistant paper base primed on its faces with a mixture ofbentonite and cooked starch and filmed on at least one primed face witha film containing greaseresistant prolamine as an essential constituent,

said film being present in amount of only about 0.4 to 2 pounds per reamsurface (2880 sq. ft.).

5. A grease-resistant paper product primed on its surface withbentonite-binder composition and filmed on such primed surface withzein, said zein containing a plasticizing agent.

6. A grease-resistant paper sheet primed on its surface withbentonite-binder composition and filmed on such primed surface withzein, said zein containing invert sugar.

'7. A paper sheet of high grease-resistance and low water-vaporpenetrability, said sheet being primed on its surface withbentonite-binder composition, being filmed on such primed surface withzein, and being waxed over said zein.

8. A paper sheet of high grease-resistance and low water-vaporpenetrability, said sheet being primed on its surface with bentonite andcooked starch, being filmed on such primed surface with zein in amountof only about 0.4 to 2 pounds per ream surface (2880 square feet), andbeing waxed over said zein with only about 2 to 4 pounds of wax per reamsurface.

9. A process of producing a grease-resistant paper product, whichcomprises priming the surface of a paper base with an aqueouscomposition containing bentonite and water-soluble binder, drying theprimed surface, filming the primed surface with an alcohol solution ofzein, and drying the filmed surface.

10. A process of producing a grease-resistant paper product, whichcomprises priming the sur, face of a paper base with an aqueouscomposition containing bentonite and cooked starch, drying the primedsurface, filming the primed sur- 5 face with an alcohol solutioncontaining zein as an essential constituent in amount to deposit onlyabout 0.4 to 2 pounds of filming substance per ream surface (2880square'feet) and drying the filmed surface. g

11. A process of producing a grease-resistan paper product, whichcomprises priming the surface of a paper base with an aqueouscomposition containing bentonite and cooked starch, drying the primedsurface, filming the primed surface with an alcohol-water solution ofzein and invert sugar, and drying the filmed surface.

thoroughly beaten state greater than that of the pulp used in kraftwrapping paper manufacture but far short of the gelatinized state ofpulp entering into glassine paper manufacture, said base being of aweight ranging from about 15 to pounds per ream surface (2880 squarefeet) and being filmed with prolamine in amount of only about 0.4 to-2.0 pounds per ream surface.

said product exhibiting flex-enduring and tearresisting qualitiesmarkedly superior to those of glassine paper of similar basis weight.

MILTON 0. SCHUR.

